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Research of the catalysts activity in the reactions of model compounds and their mutual influence was carried out. Quinoline is able to promote the hydrodesulfurization reaction of dibenzothiophene (DBT), being a source of hydrogen in the system at 260 °C. The possibility of intermolecular hydrogen transfer reactions in the reactions of tetrahydroquinoline and DBT is shown. [ABSTRACT FROM AUTHOR]

Ibuprofen is a well-established non-steroidal anti-inflammatory drug, inhibiting the prostaglandin-endoperoxide synthase. One of the key features defining the ibuprofen structure is the doubly intermolecular O–H⋯O＝C hydrogen bond in cyclic dimers as know from carboxylic acids and confirmed by X-ray analysis. Until now, there was neither information about the vaporization enthalpy of ibuprofen nor about how this thermal property is determined by the subtle balance between different types of intermolecular interaction. In this study we derive the vaporization enthalpy of ibuprofen from thermochemical experiments to be. We dissected the hydrogen bond energy, EHB = 45.0 kJ mol−1, exclusively from measured vaporization enthalpies of related aliphatic carboxylic acids, their homomorph methyl esters and alkyl acetates, respectively. This contribution from hydrogen bonding could be confirmed almost quantitatively from quantum chemical calculations of ibuprofen clusters, which also suggest dispersion interaction of similar order (Edisp = 47 kJ mol−1). Following the full analysis of the gas–vapor transition enthalpy, we studied the changing structural components from the solid to the liquid phase of ibuprofen by means of Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. The cyclic dimers as observed in the X-ray patterns are essentially preserved in the liquid state just above the melting point. However, with increasing temperature the doubly hydrogen-bonded cyclic dimers are replaced by singly hydrogen-bonded linear dimers in the liquid ibuprofen. The transfer enthalpy from the temperature-dependent equilibria of both dimers as obtained from the IR intensity ratios of the vibrational bands quantifies for the first time the energy of the released, single hydrogen bond to be EHB = 21.0 kJ mol−1. Overall, we show that a combination of thermodynamics, infrared spectroscopy and quantum chemistry provides quantification and detailed understanding of structure and molecular interaction in ibuprofen and related compounds. [ABSTRACT FROM AUTHOR]

The five fundamental units of the genetic code: uracil (U), thymine (T), cytosine (C), adenine (A) and guanine (G) are known for extremely low vapor pressure and low thermal stability at elevated temperatures. Therefore, application of conventional techniques for the determination of sublimation enthalpies and vapor pressures fails to provide accurate results. Recently, a Fast Scanning Calorimetry method (FSC) for vapor pressure determination was developed for investigation of extremely low volatile, as well as for thermally unstable molecular and ionic molecules. This success has encouraged application of the FSC method for determination of vapor pressures and sublimation enthalpies of the five nucleobases, where available literature data are in disarray. The thermodynamic data of the nucleobases available in the literature were collected, evaluated, and combined with our experimental results to reconcile available experimental data. The set of evaluated thermochemical data on the five nucleobases was recommended as the benchmark properties for these thermally labile compounds. [ABSTRACT FROM AUTHOR]

Walden's Rule is an empirical observation of an invariant fusion entropy during fusion of non-associated organic compounds. For the five nucleobases, adenine, thymine, cytosine, guanine, and uracil, surprisingly high fusion temperatures and enthalpies have been measured using a specially developed fast scanning calorimetry method that prevents decomposition. Even when nucleobases admittedly possess very high fusion temperatures, e.g. the value of 862 K measured for guanine really exceeds all expectations of the feasible dimension of the fusion temperature for such a relatively small and simple organic molecule. Hirshfeld surface analysis has been applied in order to find out an explanation for such extremely unusual thermal behavior of nucleobases. We rationalized the observed trends in terms of fusion entropy (Walden's constant = 56.5 J K−1 mol−1) as the entropic penalty of fusion not only for “non-associated”, as proposed by Walden in 1908, but also for “ideal associated” systems like nucleobases. [ABSTRACT FROM AUTHOR]

MoS2/Al2O3 and NiMoS2/Al2O3 catalysts were prepared by incipient wetness impregnation of alumina using aqueous solutions of 12-molybdophosphoric heteropolyacid and nickel citrate. Unsupported catalysts were prepared by etching a support made from MoS2/Al2O3 using hydrofluoric acid (Et-MoS2) and thermal decomposition of aluminum tetrathiomolybdate (Ref-MoS2). The activity of the catalysts in hydrodeoxygenation decreases in the series NiMoS2/Al2O3 = Et-MoS2 > MoS2/Al2O3 > Ref-NiS2. On the other hand, the selectivity relative hydrogenation of oleic acid has a different order: Et-MoS2 > MoS2/Al2O3 > Ref-MoS2 > NiMoS2/Al2O3. The unsupported Et-MoS2 catalyst has similar activity to NiMoS2/Al2O3 in hydrodeoxygenation and the highest selectivity, which indicates virtually completion of the hydrodeoxygenation reaction through a hydrogenation pathway without the formation of CO or CO2. These gases display strong inhibiting properties and have a detrimental eject on the environment. [ABSTRACT FROM AUTHOR]

Ni/Sup catalysts were prepared, where SBA-15, γ-Al2O3, SiO2 were used as supports (Sup). The synthesized catalysts were investigated by the methods of low-temperature nitrogen adsorption, temperatureprogrammed reduction (TPR), and high-resolution transmission electron microscopy. The catalytic properties of the prepared catalysts were tested in liquid phase hydrogenation of biphenyl under conditions of a flow installation at temperatures of 60-100°C, pressure of 4 MPa, volumetric feed rate of 4-10 h-1 and H2: feed ratio of 1500 nM.. A 1 wt % solution of biphenyl in heptane, as a model mixture, was used. It has been established that the activity of nickel hydrogenation catalysts depends on the nickel content and the type of support. The activity of supported nickel catalysts decreases in the series Ni-12/SBA-15 > Ni-12/SiO2 >> Ni-12/Al2O3. The kinetic characteristics of the biphenyl hydrogenation reaction were determined: the rate constants and activation energy for the hydrogenation of the first and second aromatic rings of the substrate molecule. [ABSTRACT FROM AUTHOR]

A series of catalysts have been synthesized Ni-Mo-W/P-Al2O3 with different Mo: W ratios (a sample without W, Mo: W = 2: 1, Mo: W = 1: 1, Mo: W = 1: 2, and a sample without Мо) and a concentration of P2O5 in a support of 0.5 wt %. Heteropoly acids H3PMo12O40 · nH2O and H3PW12O40 · nH2O and nickel citrate were precursors of the active phase. High-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to study the surface of the sulfide phase of the samples. Their catalytic activity was estimated in the reactions of dibenzothiophene hydrodesulfurization and naphthalene hydrogenation. A catalyst with the ratio Mo: W = 1: 1 showed the highest activity, and was characterized by the maximum concentration of atomic groups Ni-Mo-W-S, Mo-S, and W-S. [ABSTRACT FROM AUTHOR]

A series of NiMoW/P-Al2O3 catalysts with different Mo/W ratios (sample containing Mo only, Mo/W = 2: 1, Mo/W = 1: 1, Mo/W = 1: 2, and sample containing W only; P2O5 content of the support 2.0 wt %) were synthesized. The precursors of the active phase were the heteropoly acids H3PMo12O40∙nH2O and H3PW12O40∙nH2O, and also nickel citrate. The sulfide phase in the samples was studied by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy; the catalytic activity of the samples in dibenzothiophene hydrodesulfurization and naphthalene hydrogenation was determined. For the dibenzothiophene hydrogenolysis in the presence of quinoline and naphthalene (content in the model mixture, wt %: dibenzothiophene 0.3, naphthalene 1.5, and quinoline 0.5), kHDS for different samples is in the range 17.6-42.5 h-1 at 275°C and 24.6-45.9 h-1 at 300°C. For the naphthalene hydrogenation, kHYD varies from 0.79 to 1.89 h-1 at 275°C and from 0.91 to 3.78 h-1 at 300°C. The sample based on molybdenum showed the highest activity in hydrogenation and hydrodesulfurization. [ABSTRACT FROM AUTHOR]

This work presents an approach that expresses the Michaelis constant KaM and the equilibrium constant Kth of an enzymatic peptide hydrolysis based on thermodynamic activities instead of concentrations. This provides KaM and Kth values that are independent of any co-solvent. To this end, the hydrolysis reaction of N-succinyl-l-phenylalanine-p-nitroanilide catalysed by the enzyme α-chymotrypsin was studied in pure buffer and in the presence of the co-solvents dimethyl sulfoxide, trimethylamine-N-oxide, urea, and two salts. A strong influence of the co-solvents on the measured Michaelis constant (KM) and equilibrium constant (Kx) was observed, which was found to be caused by molecular interactions expressed as activity coefficients. Substrate and product activity coefficients were used to calculate the activity-based values KaM and Kth for the co-solvent free reaction. Based on these constants, the co-solvent effect on KM and Kx was predicted in almost quantitative agreement with the experimental data. The approach presented here does not only reveal the importance of understanding the thermodynamic non-ideality of reactions taking place in biological solutions and in many technological applications, it also provides a framework for interpreting and quantifying the multifaceted co-solvent effects on enzyme-catalysed reactions that are known and have been observed experimentally for a long time. [ABSTRACT FROM AUTHOR]

A new group-contribution approach involving systematic corrections for 1,4-non-bonded carbon-carbon and carbon-oxygen interactions has been proposed. Limits of the applicability of the method, associated with the highly branched structures, were established. Experimental data for enthalpies of formation in the liquid phase, enthalpies of vaporization, and enthalpies of formation in the gas phase for alkanes, alkenes, alkynes, alkylbenzenes, alkanols, ethers, ketones and aldehydes, carboxylic acids, esters, and carbonates were collected and critically evaluated through dynamic data evaluation as implemented in the NIST ThermoData Engine. An automatic procedure for molecular structure 'decomposition' was developed, and algorithms for the assessment of expanded uncertainties for the predicted property values were implemented. The combination of these software tools allows for ongoing improvements of the group-contribution parameter set as new experimental data become available. Fifty-two group-contribution parameters and their variances were evaluated for the proposed schema. Based on comparison of critically evaluated and predicted data for all classes of compounds studied, the performance of the new group formulation and associated parameters is superior to that originally suggested by Benson and the update by Cohen without an increase in the number of required parameters. [ABSTRACT FROM AUTHOR]